Acidic Sulfite Pretreatment For Improving Saccharification And Fermentation Efficiency Of Eucalyptus

The shortage of fossil fuels forced researchers worldwide to develop biofuels assubstitution of fossil energy. Bioethanol from natural lignocellulose is considered as apromising choice because it is excellent in geographical suitability, clean, environmentallyfriendly and renewable. As one of the famous fast-growing species, eucalyptus is widespreadin distribution range, highly adaptable environment and high yield. Lignocellulose biorefiningof eucalyptus has the technical and practical feasibility. Acidic sulfite pretreatment has beenproved to be effective in the size reduction of the biomass feedstock, which can significantlyimprove the cellulose accessibility. This paper focused on the enzymatic hydrolysis andfermentation processes of acidic sulfite pretreated eucalyptus materials, especially exploredmeans to enhance the enzymatic digestibility and improve the fermentation efficiency.An analysis of process variables including cellulose load, additives, substrateconcentration effect in the single-stage and multi-stage enzymatic process was carried out.The optimal cellulose load was20FPU/gcellulose. In the single-stage enzymatic hydrolysisprocess, the enzymatic hydrolysis reaction with low substrate concentration was completed in12h, but the percent digestion of cellulose (PDC) decreased rapidly with the increase ofsubstrate concentration. In high substrate concentration (30%) hydrolysis process, the glucoseconcentration could reach161.4g/L. In batches feeding multi-stage enzymatic process, theinhibition because of inhibitor accumulation can be effectively reduced, but PDC decreasedwith the increase of initial substrate concentration.In order to study the ethanol yield in the process of SHF and SSF, enzymatic hydrolyzatewas fermented using active dry yeast powder and the ethanol content was detected by theheadspace gas chromatography (HS-GC). The results showed the ethanol yield decreased withthe increase of initial glucose concentration in SHF. The ethanol concentration will be raisedif the initial substrate concentration increased, and the highest concentration of ethanol will beup to56.7g/L, which is1.7times of the SHF ethanol concentration, in the presence of24%substrate concentration. This also proved that the enzymatic hydrolysis product accumulationis the main reason for the inefficient enzymatic digestibility of high concentration hydrolysis,and additionally provided the effective means to improve the efficiency of enzymatichydrolysis.The initial adsorption of two endoglucanases (EGV and EGI) on α-cellulose wasmonitored by using the dual-wavelength ultraviolet spectroscopic method. The results showedthat the adsorption of the endoglucanase with cellulose binding domains (CBD). EGV, on the cellulose substrate is very fast. A pseudo steady state can be observed in only about4min.Equilibrium data measured by altering the initial cellulase concentration agrees extremelywell with the Langmuir isotherm model. The initial adsorption of EGV on cellulose substrateis thus probably monolayer adsorption. The adsorption of EGI is more complex. A significantdesorption occurs about every7min, and then a re-adsorption starts. It was assumed that thespecific adsorption of endoglucanase on cellulose substrate depends on the action of CBD.For EGI without CBD, the enzyme particles tend to associate with each other and deposit onthe substrate surface of fibers in the form of aggregates. Therefore, the adsorption kinetics forEGI strongly depends on its colloidal properties.The addition of surfactant polysorbate80can make the glucose yield increase, but themeasurement methods of polysorbate80in the presence of protein were infrequently reported.This work demonstrates spectrophotometric methods for rapidly analyzing polysorbate80based on the color reaction between dye and surfactant. The calibration curve was establishedfor quantitative detection of polysorbate80between absorbance of605nm and theconcentration of polysorbate80. When the BSA was present, the calibration curve wasestablished for quantitative detection of polysorbate80between the derivative absorbance of251nm and the concentration of polysorbate80.